1. Field of the Invention
This invention relates to an improved construction of a rolling mill which reduces the thickness of a workpiece, and more specifically, to means for controlling the position of segmented areas along the length of at least one work roll to compensate, and/or control its deflection caused by the rolling load.
2. Description of the Prior Art
It is well known in the metal producing industry in connection with reduction of strip or plate in a rolling mill to provide one or a combination of several devices and/or methods for compensating for roll deflection caused by the rolling forces which tend to separate the work rolls. This separation also produces a certain profile in the material, including the amount of crown and edge drop along the width of a workpiece and which affects flatness. Some of these methods and/or devices include providing: roll bending devices between the necks or ends of the work and/or back up rolls; internal hydraulically controlled roll crown; a stand where the work roll or the intermediate roll is displaced axially; and/or a central roller or a plurality of casters disposed along the length of a work roll or intermediate roll, which roller or casters are vertically displaceable relative to the work roll.
The two latter arrangements are particularly disclosed in U.S. Pat. Nos. 2,985,042 and 3,596,489. In the '042 patent, a centrally disposed roller cooperates with a cambered work roll to attempt to only control the amount of crown in the rolled product; and if it has any application to present day requirements is limited to a small range of varying width product.
The '489 patent discloses a plurality of casters mounted on a flexible beam which is acted upon by several piston cylinder assemblies to apply a counter force to the upper work roll. Even though this arrangement may be used to control both crown and edge drop across the width of the product, there are several inherent disadvantages. Since the casters are small and mounted on projections on the under side of a beam this system is limited as to the degree of rolling forces it is able to withstand, and for this reason, if it has any application, would be limited to use in the finishing rolling operation rather than in the primary operation. Secondly, since the piston cylinder assemblies contact the flexible beam along a surface opposite to where the casters are mounted, their effect involves a time lag and lost inertia, resulting in less control of the casters, and thus, less effective counter deflection action upon the work roll. Another disadvantage is in its complicated design of spaced apart separately mounted beams and the great number of casters need to span the length of the work roll.
Other systems for compensating against roll deflection appear in U.S. Pat. Nos. 4,059,976; 4,212,504; 4,222,255; and 4,480,459, which involve complicated designs either of a supporting roll with internal pressure elements which may or may not require additional roll bending means or lateral support means for the work rolls; or of an hydrostatic bearing member whereby oil is delivered directly onto the back up roll resulting in an unsightly and unsafe working environment, in addition to its undesireable marking of the product.